04-Using-Terraform-Functions-and-Other-Commands.md

04-Using Terraform Functions and Other Commands

Learning Goals

This module is designed to deepen your understanding of Terraform's capabilities by exploring both its built-in functions and a variety of advanced commands. This module is designed to deepen your understanding of Terraform's capabilities by exploring both its built-in functions and a variety of advanced commands.

Through hands-on practice, you will learn how to manipulate data and manage Terraform configurations more effectively.

Objectives

• Master the use of Terraform's built-in functions to perform data manipulation and formatting directly within Terraform configurations.

• Utilize the Terraform console for interactive exploration of function capabilities.

Step-by-Step Instructions

1 Setting Up the Terraform Console

Before experimenting with the functions, make sure you have a working Terraform setup.

• Navigate to labs/04-Using-Terraform-Functions-and-Other-Commands directory.

• Open a terminal in this directory.

• Run terraform init

• Run the Terraform console command:

  terraform console

  This opens an interactive console where you can type Terraform expressions and see their evaluated results.

2 Experiment with Terraform Functions

Here are some of the key Terraform functions and practical examples of how to use them in the Terraform console.

Numerical Functions

• abs(number): Returns the absolute value of the given number. Try this in the console:

  abs(-42)  # Outputs 42

• min(...) and max(...): Return the smallest or largest value from a list of numbers, respectively. Try these examples:

  min(5, 12, 9)  # Outputs 5
  max(5, 12, 9)  # Outputs 12

String Functions

• format(fmt, ...): Formats a string according to the specified format string fmt. Here's how you use it:

  format("Hello, %s!", "world")  # Outputs "Hello, world!"

• join(delimiter, list): Concatenates the elements of a list into a single string, inserting the delimiter between elements. Example:

  join("-", ["foo", "bar", "baz"])  # Outputs "foo-bar-baz"

• lower(string) and upper(string): Convert a string to all lower or upper case, respectively. Examples:

  lower("TERRAFORM")  # Outputs "terraform"
  upper("terraform")  # Outputs "TERRAFORM"

Collection Functions

• concat(list1, list2, ...): Combines multiple lists into a single list. Example:

  concat(["a", "b"], ["c"])  # Outputs ["a", "b", "c"]

• contains(list, value): Checks if a list contains a given value. Example:

  contains(["a", "b", "c"], "a")  # Outputs true

• element(list, index): Retrieves the element at a specified index in a list. Example:

  element(["a", "b", "c"], 1)  # Outputs "b"

• lookup(map, key, default): Retrieves the value of a specified key from a map. Example:

  lookup({"a" = "apple", "b" = "banana"}, "a", "unknown")  # Outputs "apple"

Encoding and Template Functions

• base64decode(string) and base64encode(string): Decode or encode in Base64. Example:

  base64encode("hello world")  # Outputs "aGVsbG8gd29ybGQ="
  base64decode("aGVsbG8gd29ybGQ=")  # Outputs "hello world"

• jsonencode(value) and jsondecode(string): Convert a value to JSON string or parse a JSON string to a Terraform structure. Example:

  jsonencode({"key" = "value"})  # Outputs "{\"key\":\"value\"}"
  jsondecode("{\"key\": \"value\"}")  # Returns {"key" = "value"}

3 Exiting the Console

To exit the Terraform console, simply type exit and press Enter, or press Ctrl + C.

4 Practice Terraform Commands

After exploring Terraform functions, we'll practice using several important Terraform CLI commands that will help you manage and interact with the configuration effectively. Below are explanations and step-by-step instructions for each command using your current Terraform setup.

Navigate to the directory

Before executing the commands, make sure you are in the correct directory labs/04-Using-Terraform-Functions-and-Other-Commands where a Terraform configuration file is located.

The terraform configuration is to create a random string.

The content of the file main.tf looks like below

terraform {
  required_version = "~> 1.8.0"  # Specifies the required Terraform version
  required_providers {
    random = {
      source  = "hashicorp/random"
      version = "3.4.3"
    }
  }
}

resource "random_string" "randomname" {
  length  = 16
  count   = 2
  special = false
  upper   = false
}

output "random_string_values" {
  value = random_string.randomname.*.result
  description = "The generated random strings."
}

Terraform Commands to Practice

• terraform validate: Ensures that the configuration is syntactically valid and internally consistent.

  terraform validate

• terraform fmt: Automatically reformat your configuration in the standard style.

  terraform fmt

To effectively show how terraform validate and terraform fmt work, you can start by introducing a deliberate syntax error or formatting inconsistency in your Terraform configuration.

For instance, let's modify the main.tf file to include a misalignment and a small error:

resource "random_string" "randomname" {
length = 16  # Improperly formatted line (should be indented)
count   = 2
special = false
uper    = false  # Typo here should be "upper"
}

First, demonstrate how terraform fmt can automatically correct formatting issues:

terraform fmt

This command will adjust the indentation for the length line but won't fix the typo in uper. You can show the changes by displaying the file content

Next, use terraform validate to check for configuration errors:

terraform validate

This command will output an error due to the typo in the attribute name (uper instead of upper). The output might look something like this:

Error: Unsupported argument

  on main.tf line 4, in resource "random_string" "randomname":
   4: uper    = false

An argument named "uper" is not expected here. Did you mean "upper"?

After identifying the error with terraform validate, correct the typo in the main.tf file:

resource "random_string" "randomname" {
  length  = 16
  count   = 2
  special = false
  upper   = false  # Corrected typo
}

• terraform output: Shows the outputs defined in your configuration. This is useful after an apply to retrieve the values of outputs.

  terraform apply
  terraform output

• terraform show: Provides human-readable output from a state or plan file. Use this to inspect the current state.

  terraform show

• terraform version: Displays the current Terraform version.

  terraform version

• terraform get: Downloads and installs modules needed for the configuration.

  terraform get

• terraform graph:

In a subsequent exercise, you will have the opportunity to explore the terraform graph command. This command produces a visual representation of either a configuration or execution plan. The output is in DOT format, which can be used by GraphViz to generate charts. This visual tool can be incredibly helpful for understanding the relationships between resources in your Terraform configurations and for identifying dependencies and their execution order.

terraform graph > graph.dot

dot -Tpng graph.dot -o graph.png

Congratulations

This hands-on session with Terraform's built-in functions and commands provides a deeper understanding of how to dynamically manage and manipulate data within Terraform configurations.

To read more of Terraform's functions and to see a complete list of available functions, visit the Terraform Documentation on Functions.